We live in a multisensory world, which requires us to continually, dynamically, and effectively process stimuli from across the sensory modalities. To do so successfully, we need to integrate corresponding unisensory stimulus components together to perceive coherent multisensory objects, while also appropriately segregating out concurrent non-corresponding stimuli. In the next period of this grant, we propose a new set of studies to continue our programmatic investigation of the mechanisms by which attention and related cognitive factors facilitate effective functioning in complex multisensory environments. In particular, we will investigate three fundamental facets of these mechanisms. First, we will study the influence of the top-down cognitive factors of spatial attention and reward prospect on multisensory (auditory/visual) integration and segregation processes. Second, we will examine the commonality across the auditory and visual modalities of the mechanisms underlying rapid attentional target-search processes in complex stimulus environments, including the cross- modality coupling of such attentional processes. Third, we will investigate the multisensory integration and segregation processes when input from one particular modality is relevant, but there is conflicting concurrent input from a second modality; we will also compare these crossmodal processes to those invoked in response to conflicting input from within the same modality. As before, we will use a combination of behavioral measures, oscillatory electroencephalography (EEG), event-related potentials (ERPs), and functional MRI (fMRI) to perform these studies, with the aim to delineate the timing, sequence, and location of underlying neural processes. Additionally, we will acquire EEG and fMRI measures of brain activity simultaneously for several of the proposed experiments using our new MR- compatible EEG system purchased via a supplement from this project. Such an approach will enable us to perform trial-to-trial covariational analyses on the EEG and fMRI data patterns, providing powerful new ways to link the high-temporal-resolution EEG signals to the associated cortical generators measured in the fMRI. Moreover, the simultaneous recording will also allow us to examine the modulating influence on the cortical EEG of the subcortical brain regions involved in attention, reward, and multisensory integration but whose influence cannot be assessed with EEG alone. Thus, these experiments will delineate with unprecedented precision the neural mechanisms by which attention and related cognitive functions enable successful navigation of our complex multisensory world.